This invention relates to a composition resistant to radiations such as ultraviolet rays, electron beams, ion beams or X-rays and a process for forming a pattern by using the same. More particularly, this invention relates to a radiation-sensitive composition suitable for use in fine processing and excellent in resistance to dry etching and a process for forming a pattern by using the same.
In recent years, oxygen reactive-ion etching (RIE) techniques utilizing a resist material have been attempted. For example, an attempt has been made to etch insulation layers of semiconductors or the like by oxygen RIE. However, conventional resist materials themselves are lacking in resistance to oxygen RIE, so that they are lost or deformed by etching before the etching of the layer to be processed is completed.
Besides, in the fine processing of semiconductor elements, the substrates have a complicated unevenness in surface levels. In order for a resist film to cover such unevenness and withstand the subsequent dry etching step, it is preferable that the resist film has the largest possible thickness. On the other hand, the resolution of a resist depends on its thickness and it is desirable that the resist is thinner. As minimum feature sizes are reduced, it becomes more and more difficult to fulfil these contradictory requirements by using a single-layer resist system. In order to overcome these problems, a variety of multilayer resist systems were proposed. The two-layer resist system of this invention is also one of these multilayer systems. The structure comprises a lower thick flat layer and an upper resist film layer, and a film resistant to oxygen RIE is used as the resist film. However, no resist film that has high resolution and high practicality as well as resistance to oxygen RIE has been available.
An example of a resist having some resistance to oxygen RIE is a positive resist containing a polysilsesquioxane (Japanese Patent Laid-Open No. 14161/1982). However, when this resist contains 10 wt. % or more of the polysilsesquioxane, the resolution is worsened. When it contains below 10 wt. % of the polysilsesquioxane, the resistance to oxygen RIE is not fully satisfactory.